US20140362875A1 - Method and device for optical transmission at adaptive effective rates - Google Patents

Method and device for optical transmission at adaptive effective rates Download PDF

Info

Publication number
US20140362875A1
US20140362875A1 US14297469 US201414297469A US2014362875A1 US 20140362875 A1 US20140362875 A1 US 20140362875A1 US 14297469 US14297469 US 14297469 US 201414297469 A US201414297469 A US 201414297469A US 2014362875 A1 US2014362875 A1 US 2014362875A1
Authority
US
Grant status
Application
Patent type
Prior art keywords
optical
transmission
digital data
terminal
signal
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
US14297469
Other versions
US9967047B2 (en )
Inventor
Arnaud LE KERNEC
Mathieu DERVIN
Michel Sotom
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Thales SA
Original Assignee
Thales SA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date

Links

Images

Classifications

    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04JMULTIPLEX COMMUNICATION
    • H04J14/00Optical multiplex systems
    • H04J14/02Wavelength-division multiplex systems
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B10/00Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/11Arrangements specific to free-space transmission, i.e. transmission through air or vacuum
    • H04B10/112Line-of-sight transmission over an extended range
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B10/00Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/11Arrangements specific to free-space transmission, i.e. transmission through air or vacuum
    • H04B10/118Arrangements specific to free-space transmission, i.e. transmission through air or vacuum specially adapted for satellite communication
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B10/00Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/25Arrangements specific to fibre transmission
    • H04B10/2575Radio-over-fibre, e.g. radio frequency signal modulated onto an optical carrier
    • H04B10/25752Optical arrangements for wireless networks
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B10/00Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/29Repeaters

Abstract

A method for transmitting digital data by a primary optical signal between a transmitter terminal and a receiver terminal, involves the following steps: determining a magnitude characterizing optical-wave degradation between the transmitter terminal and the receiver terminal, determining a number of transmission channels by a decreasing function of the magnitude characterizing optical-wave degradation, distributing the digital data over the transmission channels, modulating optical signals of different wavelengths using digital data distributed over the transmission channels, generating the primary optical signal by wavelength multiplexing of the optical signals, and sending a transmission configuration, including at least the number of transmission channels, from the transmitter terminal to the receiver terminal.

Description

    CROSS-REFERENCE TO RELATED APPLICATION
  • This application claims priority to foreign French patent application No. FR 1301304, filed on Jun. 7, 2013, the disclosure of which is incorporated by reference in its entirety.
  • FIELD OF THE INVENTION
  • The present invention relates to a method for transmitting an optical signal in which the effective data rate is adapted as a function of the disturbances on the propagation channel. The invention also relates to an optical-signal transmission device designed to implement such a method.
  • BACKGROUND
  • Communication by optical signal is a known technology that uses the propagation of light to transmit information over a communication channel between two remote points. It is already used to exchange information between satellites or between a satellite and a fixed terminal on the earth, and is commonly used in terrestrial fiber-optic telecommunication networks. An optical signal, for example a laser beam modulated by effective data, is sent from a transmitter terminal to a receiver terminal. In general, the communication channel of an optical transmission device can be empty space (the atmosphere, space), the marine environment, an optical guide or any other medium that is transparent to light. The conditions for transmitting an optical signal through these different media may vary over time or space. These disturbances cause a deterioration in the quality of the optical signal received by the receiver terminal (attenuated signal, random phase) and are liable to alter the data being transmitted.
  • As shown in FIG. 1, a satellite S is fitted with a transmitter terminal TE that sends digital data to a receiver terminal TR located on the earth T using a primary optical signal S1. The terrestrial atmosphere may disturb the propagation of the signal between the two terminals and thereby cause transmission errors in the digital data. Various techniques have been developed to adapt the optical transmission to the disturbances P on the communication channel. Document FR2957214, which describes an optical transmission method using laser signals in which an encoding rate of the digital data sent by a laser signal is adapted as a function of the propagation conditions of the laser beam, is in particular known. To take account of the effect of these disturbances P on the optical transmission, the use of a secondary optical signal S2, sent by the receiver terminal and received by the transmitter terminal, is known. The propagation conditions of the optical signal, characterized by the secondary optical signal S2 received by the transmitter terminal, make it possible to adapt the encoding rate, and therefore the effective rate, in real time. A low encoding rate is used for highly disturbed optical transmission, so the effective digital data in the signal sent has a greater degree of redundancy.
  • The adaptation of the effective rate according to known solutions only enables transmission to be maintained for disturbances of moderate amplitude or, when it relates to interlacing, for significant disturbances of limited duration. If significant attenuation occurs, or attenuation occurs over an excessively long period in relation to the foreseeable interlacing periods in practice, these known solutions do not provide a satisfactory effective rate. It is therefore desirable to use an optical transmission method that makes it possible to adapt and optimize the effective rate transmitted over an extended range of disturbances on the transmission channel, while enabling fine tuning of adaptation of the effective rate within this range.
  • SUMMARY OF THE INVENTION
  • The invention is intended to propose an alternative solution that overcomes these difficulties by implementing both wavelength multiplexing and variable-rate encoding to best adapt the effective rate over an extended range of variations in the propagation conditions of the optical wave.
  • For this purpose, the invention relates to a method for transmitting digital data using a primary optical signal between a transmitter terminal and a receiver terminal, characterized in that it involves the following steps:
    • determining a magnitude characterizing optical-wave degradation between the transmitter terminal and the receiver terminal,
    • determining a number of transmission channels by means of a first stepwise decreasing function of the magnitude characterizing optical-wave degradation,
    • distributing the digital data over the transmission channels,
    • modulating optical signals of different wavelengths, of which there are as many as there are transmission channels; each of the respective optical signals being modulated by digital data distributed respectively to one of the transmission channels,
    • generating the primary optical signal by means of wavelength multiplexing of the optical signals,
    • sending a transmission configuration from the transmitter terminal to the receiver terminal; the transmission configuration including at least the number of transmission channels.
  • The invention also relates to a device for transmitting digital data using a primary optical signal including a transmitter terminal and a receiver terminal; said transmitter terminal including:
    • a processor including means for distributing and sending digital data over transmission channels,
    • optical sources that are able to send optical signals of different wavelengths; each of the optical sources having means to modulate the optical signal of said optical source as a function of digital data sent by the processor over a transmission channel,
    • a wavelength multiplexer able to generate the primary optical signal by wavelength multiplexing of optical signals sent by the optical sources;
    • means for determining a magnitude characterizing optical-wave degradation between the transmitter terminal and the receiver terminal,
    • a distribution module, implemented in the processor, that is able to distribute the digital data over a number of transmission channels that is less than or equal to the number of optical sources,
    • a control module, implemented in the processor, that is able to determine the number of transmission channels by means of a stepwise decreasing function of the magnitude characterizing optical-wave degradation,
    • activation means for a number of optical sources equal to the number of transmission channels; the primary optical signal being generated by multiplexing the optical signals sent by the optical sources thus activated; each of the optical signals being modulated by digital data.
    BRIEF DESCRIPTION OF THE DRAWINGS
  • The invention is further explained and other advantages given in the detailed description of the embodiments given by way of example in the following figures:
  • FIG. 1, already mentioned, shows an example of optical transmission between a satellite and the earth, in which the method can be implemented,
  • FIG. 2 shows the main functional modules of an optical-transmission transmitter terminal according to the invention,
  • FIG. 3 shows the main modules of an optical-transmission receiver terminal according to the invention,
  • FIGS. 4 a and 4 b show the functional architecture of a transmitter terminal and of a receiver terminal respectively according to a first embodiment of the invention,
  • FIGS. 5 a and 5 b show the functional architecture of a transmitter terminal and of a receiver terminal respectively according to a second embodiment of the invention,
  • FIG. 6 shows the functional architecture of a receiver terminal according to a third embodiment of the invention,
  • FIG. 7 shows the operating principle of an optical transmission method according to the known prior art,
  • FIGS. 8 a and 8 b show the operating principle of an optical transmission method according to two variants of the invention.
  • For the sake of clarity, the same elements are marked with the same reference signs in all of the figures.
  • DETAILED DESCRIPTION
  • A device for transmitting digital data by optical signal includes firstly a transmitter terminal TE, of which the main functional modules are shown in FIG. 2, and secondly a receiver terminal TR, of which the main functional modules are shown in FIG. 3.
  • According to FIG. 2, the transmitter terminal TE includes:
    • a processor 10 including means for distributing and sending digital data 11 over transmission channels 13,
    • optical sources 14 that are able to send optical signals 15 of different wavelengths; each of the optical sources 14 having means to modulate the optical signal 15 of said optical source 14 as a function of digital data 11 sent by the processor 10 over a transmission channel 13,
    • a wavelength multiplexer 16 able to generate an optical signal 17 by wavelength multiplexing of optical signals 15 sent by the optical sources 14;
    • an optical power amplifier 18 able to generate a primary optical signal S1 by amplification of the optical signal 17 sent by the wavelength multiplexer 16,
    • an optical interface 19 for transmitting the primary optical signal S1 to the receiver terminal TR.
    • An optical interface 20 for receiving a secondary optical signal S2 sent by the receiver terminal TR; a magnitude 12 characterizing optical-wave degradation between the transmitter terminal TE and the receiver terminal TR being measured by receipt of the optical signal S2 sent by the receiver terminal TR to the transmitter terminal TE. It should be noted at this stage that this optical receiver interface 20 is an option for the device according to the invention; if predictions regarding this degradation are available, this optical receiver interface 20 need not be implemented,
    • a device 100 for sending a tertiary signal S3 to the receiver terminal TR, in which the tertiary signal S3 carries a transmission configuration 102 enabling the receiver terminal TR to process the effective data 11 sent via the primary optical signal S1. As detailed below, the transmission configuration 102 includes at least the number of transmission channels 13 implemented for transmission of the effective data, such as to enable the primary optical signal S1 to be processed by the receiver terminal TR. It should be noted at this stage that this transmission device 100 is an option for the device according to the invention. Details are given below of the alternative options enabling transmission of the transmission configuration 102 between the two terminals; these alternative options not requiring implementation of the transmission device 100.
  • According to FIG. 3, the receiver terminal TR includes:
    • an optical interface 21 for receiving the primary optical signal S1 sent by the transmitter terminal TE,
    • an optical amplifier 22 able to generate an optical signal 23 by amplifying the primary optical signal S1,
    • a wavelength demultiplexer 24 that is able to generate optical signals 25 of different wavelengths by demultiplexing the optical signal 23,
    • converters 26 that are able to convert each of the optical signals 25 of different wavelengths into electrical signals 27,
    • a processor 28, including means for recombining electrical signals 27 to reconstitute digital data 11 sent by the transmitter terminal TE,
    • an optical source 29 and an optical transmission interface 30 able to send the secondary optical signal S2 to the transmitter terminal TE. As is the case with the optical receiver interface 20, implementing this optical transmission interface 30 is an option for the present invention. If predictions regarding degradation of the optical wave are available, this optical receiver interface 30 need not be implemented,
    • a device 101 for receiving the tertiary signal S3 sent by the transmitter terminal TE, in which the tertiary signal transmits the transmission configuration 102 to enable the primary optical signal S1 to be processed by the receiver terminal TR. As is the case for the transmitter device 100, implementation of the receiver device is optional in the present invention. Details of alternative options that do not require implementation of the receiver device 101 are given below.
  • The conditions for transmitting the optical wave between the transmitter terminal TE and the receiver terminal TR are determined by the transmitter terminal by means of a reception characteristic of the secondary optical signal S2, referred to as the magnitude 12 characterizing optical-wave degradation between the transmitter terminal TE and the receiver terminal TR. This provides the transmission device, in real time, with a magnitude representing the transmission conditions, enabling it to continuously adapt transmission of the digital data. Thus, the transmitter terminal according to the invention includes means for measuring a magnitude 12 characterizing optical-wave degradation between the transmitter terminal TE and the receiver terminal TR. Advantageously, the magnitude 12 characterizing optical-wave degradation is a reception power or a reception direction of the secondary optical signal S2 received by the transmitter terminal TE. In an alternative embodiment, the transmission conditions of the optical wave between the transmitter terminal TE and the receiver terminal TR are also known and progress in a predetermined manner. They may for example be predicted on the basis of knowledge of the trajectory of the satellite.
  • The transmission device logically includes the same number of optical sources 14 and converters 26, referred to as the maximum number of transmission channels Nmax. As detailed below, the transmission device makes it possible to cover a disturbance range that gets wider as the maximum number of transmission channels Nmax increases. However, if this number is too high, the hardware issue becomes more complicated.
  • The invention relates firstly to an optical transmission method that adapts the number of wavelengths multiplexed to the transmission conditions of the optical wave between the transmitter terminal and the receiver terminal. To do so, the method according to the invention includes the following steps:
    • determining a magnitude 12 characterizing optical-wave degradation between the transmitter terminal TE and the receiver terminal TR,
    • determining a number Nλ of transmission channels 13 by means of a first stepwise decreasing function of the magnitude 12 characterizing optical-wave degradation,
    • distributing the digital data 11 over the transmission channels 13,
    • modulating optical signals 15 of different wavelengths, of which there are as many Nλ as there are transmission channels; each of the respective optical signals 15 being modulated by digital data 11 distributed respectively to one of the transmission channels 13,
    • generating the primary optical signal (S1) by means of wavelength multiplexing of the optical signals 15.
    • sending a transmission configuration 102 from the transmitter terminal TE to the receiver terminal TR; the transmission configuration 102 including at least the number Nλ) of transmission channels 13.
  • During a digital-data transmission session between the transmitter terminal and the receiver terminal, the method adapts, in real time, the number of transmission channels 13 to suit the transmission conditions. Thus, if the transmission conditions are good, the method uses a high number Nλ of transmission channels, for example a number equal to the maximum number of transmission channels Nmax. The bit rate of the optical signal obtained following multiplexing is equal to the sum of the bit rates of the optical sources, the optical power delivered by the amplifier 18 is shared between the different optical sources 14 used. If the transmission conditions deteriorate, it is possible to maintain the quality of the signal by using fewer transmission channels 13. After the amplification step, the optical power of the primary optical signal S1 delivered by the amplifier 18 is then concentrated on fewer optical sources 14, helping to improve the received signal-noise ratio and thereby to reduce the bit error rate of the digital data received by the receiver terminal.
  • To improve transmission quality, it is also possible to encode the digital data to be sent. Encoding typically involves adding redundancy to the digital data sent in relation to the effective information. For example, in the case of systematic codes, this redundancy may involve adding parity bits to detect potential errors in the effective signal received after transmission. The bit rate transmitted is then the sum of the effective bit rate, which corresponds to the binary volume of the effective information, and of the redundant bit rate resulting from the encoding operation. In general, for systematic or non-systematic codes, the encoding rate η is defined as the ratio between the effective bit rate and the output bit rate transmitted from the encoder, i.e. after encoding.
  • Advantageously, the method includes the following steps:
    • determining an encoding rate η, using a second decreasing function of the magnitude 12 characterizing optical-wave degradation,
    • encoding the digital data 11 distributed to each of the transmission channels 13 according to the previously determined encoding rate η;
  • In this case, the transmission configuration 102 includes, in addition to the number Nλ of transmission channels 13, the encoding rate η, to enable adapted decoding of the effective data received by the receiver terminal TR.
  • Another technique for processing digital data involves interlacing the data to be transmitted. This technique makes it possible to extend the correction capacity of certain error-correcting codes to longer erroneous bit sequences than if the error-correcting code is used on its own. Such erroneous bit sequences may occur if the transmission conditions are highly degraded for a relatively long period of time. The principle of interlacing is to mix up the encoded bits before transmission according to a predetermined scheme, and then to put them back into order on receipt, before decoding, using the same scheme. Accordingly, signal samples significantly affected by a long-lasting attenuation episode in the propagation channel are spread throughout shorter erroneous sequences that do not exceed the correction capacities of the code used.
  • Advantageously, the method includes an interlacing step for the digital data 11 distributed to each of the transmission channels 13. In this case, the transmission configuration 102 also includes the number Nλ of transmission channels 13, and possibly the encoding rate η, configuration information on the interlacing method used, to enable adapted de-interlacing of the effective data received by the receiver terminal TR. Such configuration information enables the interlacing to be optional, or even enables a choice from several predefined interlacing functions. The transmission configuration need not be sent if the interlacing is determined by the waveform.
  • To send the transmission configuration 102 to the receiver terminal, a first option was mentioned involving implementing, on the transmitter terminal TE, a device 100 for sending a tertiary signal S3 to a receiver device 101 of the receiver terminal TR. Advantageously, the tertiary signal S3 may be an optical signal with a wavelength different to all of those already used for transmitting the actual effective data, i.e. different from the wavelengths of the optical signals 15 carrying the effective data 11. In this case, the transmitter device 100 may include a laser source, a modulation function for the optical signal, an encoding function, possibly a power amplifier, and possibly an optical interface enabling coupling to the propagation environment, for example a secondary telescope in the case of spatial optical transmission. It should also be noted that the optical interface of the device 100 for transmitting the tertiary signal S3 may be combined with the optical interface 20 for receiving the secondary signal S2.
  • Upon receipt, the receiver device 101 therefore includes a reception interface, for example a telescope, and possibly an incoming amplification, demodulation and decoding function. This optical transmission is preferably low rate, thereby enabling a very high encoding rate and a link that is much more robust to the disturbances P on the communication channel. Thus, in the event of very high degradation of the transmission conditions, loss of the transmission link of the transmission configuration 102 necessarily means that the transmission conditions are too poor for transmission of effective data. It should be noted that this additional transmission device can also perform other functions, such as lock-on beacon for the direction, acquisition and tracking system of the receiver terminal.
  • In an alternative embodiment, the tertiary signal S3 may be a hyperfrequency signal. In this case, known satellite-ground transmission techniques can advantageously be used since the quantity of data to be transmitted, i.e. the content of the transmission configuration 102, is in this case very small, and therefore the transmission thereof does not give rise to any particular difficulty.
  • Alternative options enabling the transmission configuration 102 to be sent to the receiver terminal that do not require implementation of the transmitter or receiver devices 100, 101 for the tertiary signal S3, are also described below.
  • FIGS. 4 a and 4 b show the functional architecture of a transmitter terminal and of a receiver terminal respectively according to a first embodiment of the invention.
  • As described above, the transmitter terminal of the transmission device includes a processor 10 used to distribute the digital data 11. The device thus includes a distribution module 40, also referred to as paralleling, implemented in the processor 10 and able to distribute the digital data 11 over a number Nλ of transmission channels 13 that is less than or equal to the maximum number of transmission channels Nmax. During a communication session, the number Nλ of transmission channels 13 is variable and adjusted as a function of the magnitude characterizing wave degradation. A control module 41, implemented in the processor 10, is able to determine this number Nλ of transmission channels 13 by means of a first stepwise decreasing function of the magnitude 12 characterizing optical-wave degradation.
  • The processor 10 also includes encoding and/or interlacing modules 42 for the digital data 11 distributed to each of the transmission channels 13. During a communication session, the encoding rate η used for each of the encoding modules 42 is variable and adjusted as a function of the magnitude 12 characterizing optical-wave degradation. The control module 41 is able to determine this encoding rate η using a second decreasing function of the magnitude 12 characterizing optical-wave degradation.
  • The effective data 11 distributed over the transmission channels 13, and preferably encoded and interlaced, are then used to modulate optical signals 15 generated by optical sources 14. The device therefore includes means for activating a number of optical sources 14 equal to the number Nλ of transmission channels 13. These activation means notably include optical switches that enable an optical beam to be emitted from an optical source supplied with digital data distributed to a transmission channel 13.
  • The primary optical signal S1 is then generated by multiplexing the optical signals 15 emitted by the optical sources 14 activated by said activation means, and each of the optical signals 15 is modulated by digital data 13. The wavelength multiplexer 16 is marked WDM on FIG. 4 a, which stands for Wavelength Division Multiplexing. The optical power of the optical signal 17 transmitted by the multiplexer 16 may be amplified before transmission according to a predefined total optical power.
  • As described above, the transmission configuration 102 can be sent using a dedicated device and a tertiary signal S3. It can also be sent using the primary optical signal S1. FIGS. 4 a and 4 b show this case of transmission by the primary optical signal S1 according to a first possible embodiment. In this first embodiment, the transmission configuration 102, which includes at least the number Nλ of transmission channels and, where applicable, the encoding rate and/or configuration information regarding the interlacing method, is determined by the control module 41 and sent to an encoding module 103, before being inserted into one of the optical carriers by time-division multiplexing (module 104 in FIG. 4 a). Thus, the method advantageously includes a time-division multiplexing step, after encoding, of the transmission configuration 102 and of the effective data 11 distributed to one of the transmission channels 13, possibly followed by an interlacing step (module 105 on FIG. 4 a) for the data outputted from the multiplexer. It is possible to use different encoding rates for the two data streams (transmission configuration and effective data) to make transmission of the configuration information more robust. Given the very low rate required to send this configuration information, the impact on the effective rate is very limited. To prevent one of the channels from being singled out in relation to the others, as shown in FIG. 4 a, the architecture of the channel, including the time-division multiplexer, can be duplicated, at transmission and reception, and applied to all the channels in order to simplify data paralleling by making all of the paths identical. Furthermore, given that the configuration information represents a limited volume of data, it has a small impact on the effective data rate.
  • The receiver terminal of the transmission device has a functional “mirror” architecture of the functional architecture of the transmitter terminal. Thus, following the step involving wavelength demultiplexing and conversion of the optical information into digital information (converters 26), the method includes a de-interlacing and decoding step for each of the electrical signals 27. In this first embodiment, the transmission configuration 102 is reconstituted during this de-interlacing and decoding step, carried out on the channel carrying the transmission configuration 102. This transmission configuration, sent to the control module 45 of the processor 28, enables the de-interlacing and decoding modules 43 to be provided with the information required, notably the encoding rate and the configuration information for the interlacing method used in the transmitter terminal. Moreover, the number Nλ of transmission channels is provided to a serialization module 44, which is able to reconstitute the digital data 11 by adapting in real time to a variable number of transmission channels. In other words, the method includes a reconstitution step for the digital data 11 received by the receiver terminal configured in real time using the transmission configuration.
  • FIGS. 5 a and 5 b show the functional architecture of a transmitter terminal and of a receiver terminal respectively according to a second embodiment of the invention. This second embodiment includes several modules identical to those shown in FIGS. 4 a and 4 b. These modules, shown in FIGS. 5 a and 5 b, are not described again. The second embodiment is different from the first on account of the means used to send the transmission configuration 102. In this second case, the latter is sent to the receiver terminal by overmodulation of one of the optical carriers using the functional module 110 referred to as an analogue overmodulation module. Low-frequency overmodulation is notably used, typically around 10 kHz to 10 MHz, superposed on the high-rate effective data in the form of a pilot tone, or a radio-frequency subcarrier placed outside the baseband spectrum of the electrical signal. Given the digital modulation of the signal used to transmit the effective data, this signal is hardly, if at all, disturbed by adding low-amplitude analogue overmodulation, typically around a few percent, containing information on the configuration used (wavelength number, encoding rate, etc.). In particular, a subcarrier with frequency modulation can be used to encode the configuration used. In the receiver terminal, as shown in FIG. 5 b, the transmission configuration is reconstituted by appropriate filtering in the electrical domain, i.e. after optical/electrical conversion, using a converter 26. Thus, the method advantageously includes an analogue overmodulation step for one of the optical signals 15 using the transmission configuration 102.
  • FIG. 6 shows the functional architecture of a receiver terminal according to a third embodiment of the invention. In this embodiment, the transmission configuration is reconstituted using a dedicated optical/electrical converter 120. Finally, it should be noted that another possible embodiment involves using an additional wavelength exclusively to implement an out-band signaling channel. Given the very low rate required to send this signaling information, the power of this signal can be very low in relation to the wavelengths used for sending the effective data, thereby having no negative impact on the optical power of the effective data signals. Indeed, the optical amplifier works at a constant output optical power and distributes the power between the different wavelengths used. This latter embodiment has the drawback of requiring a specific wavelength to send the transmission configuration 102, but has the advantage of having no impact on the channels used to send the effective data 11.
  • FIG. 7 shows the operating principle of an optical transmission method according to the known prior art, in which the encoding rate is adapted. FIG. 8 a shows the operating principle of an optical transmission method according to a first aspect of the invention in which the number of transmission channels is adapted to the transmission conditions. FIG. 8 b shows the operating principle of an optical transmission method according to a second aspect of the invention in which the encoding rate and the number of transmission channels are adapted to the transmission conditions.
  • These three figures show the effective data rate as a function of the optical losses between the transmitter terminal and the receiver terminal. For these three empirical figures, a bit error rate close to zero is required on reception, and a threshold value after decoding of 10−12, representing a known requirement, is used. In FIG. 7, the transmission device includes an optical source with a nominal gross rate (including redundancy bits inserted by the error-correcting code) of 40 Gigabits per second (Gbps). A variable encoding rate adjusted as a function of optical losses is used. An encoding rate of 90% is used for zero optical losses, in which case the effective data rate is 36 Gbps. As the optical losses increase, the encoding rate is reduced to keep a near-zero bit error rate. This technique, which is effective for moderate-amplitude optical losses, becomes ineffective for more significant optical losses.
  • In FIG. 8 a, the transmission device includes four optical sources each having a nominal gross rate of 10 Gbps and multiplexing means. For limited optical losses, the method according to the invention uses a high number of transmission channels, and the effective rate is distributed over four wavelengths. A fixed encoding rate of 90% is used for each of the transmission channels. For zero optical losses, the effective data rate is then 36 Gbps. As optical losses increase, the method reduces the number of transmission channels. For high optical losses, for example between 4 and 6 dB, a single optical source is used.
  • The transmission device in FIG. 8 b also includes four sources each having a nominal rate of 10 Gbps. In this case, the device also includes multiplexing means and variable-rate encoding means. For limited optical losses, the method according to the invention uses a high number of transmission channels, and the effective rate is distributed over four wavelengths. As the optical losses increase, the encoding rate is progressively reduced. If these optical losses are greater than a predetermined threshold, the method according to the invention uses fewer transmission channels. Thus, the envelope curve 60 in FIG. 8 b may be used in the control module 41 of the processor 10 to determine, at each instant, the number of transmission channels 13 and the encoding rate η.
  • Thus, adaptation of the encoding rate advantageously enables the effective rate to be adjusted for relatively small variations in the transmission conditions. The combination of adaptation of the number of multiplexing channels and of the encoding rate enables both coverage of an extended range of transmission conditions and fine tuning of the effective rate within this range. This configuration is particularly advantageous, for example in the case of a satellite used to relay data. During a communication session, the satellite has to transmit a volume of data, for example images, to a fixed terrestrial terminal. This type of satellite is generally in low orbit, the duration of a communication session is short, and it is beneficial to optimize data transfer during the period. The method selects a suitable number of channels as a function of the transmission conditions measured at each instant of the communication session. To optimize the effective rate while keeping the error rate within acceptable limits, the method also adjusts the effective rate using the encoding rate. This dual adaptation advantageously enables the effective rate to be optimized for a given available optical power, for example that delivered by an optical amplifier used in saturation.

Claims (17)

  1. 1. A method for transmitting digital data by a primary optical signal between a transmitter terminal and a receiver terminal, comprising the following steps:
    determining a magnitude characterizing optical-wave degradation between the transmitter terminal and the receiver terminal,
    determining a number of transmission channels by means of a first stepwise decreasing function of the magnitude characterizing optical-wave degradation,
    distributing the digital data over the transmission channels,
    modulating optical signals of different wavelengths, of which there are as many as there are transmission channels; each of the respective optical signals being modulated by digital data distributed respectively to one of the transmission channels,
    generating the primary optical signal by means of wavelength multiplexing of the optical signals, and
    sending a transmission configuration from the transmitter terminal to the receiver terminal; the transmission configuration including at least the number of transmission channels.
  2. 2. The method as claimed in claim 1, including the following steps:
    determining an encoding rate, using a second decreasing function of the magnitude characterizing optical-wave degradation,
    encoding the digital data distributed to each of the transmission channels according to the previously determined encoding rate;
    the encoding rate being defined as a ratio between an effective bit rate and an output bit rate transmitted from the encoder; the transmission configuration also including the encoding rate.
  3. 3. The method as claimed in claim 1, including an interlacing step for the digital data distributed to each of the transmission channels; the transmission configuration also including information relating to interlacing configuration.
  4. 4. The method as claimed in claim 1, in which the magnitude characterizing optical-wave degradation is determined by measuring, at the transmitter terminal, a secondary optical signal sent by the receiver terminal and received by the transmitter terminal.
  5. 5. The method as claimed in claim 1, in which the magnitude characterizing optical-wave degradation is determined by calculation using a predetermined function.
  6. 6. The method as claimed in claim 1, including a time-division multiplexing step for the transmission configuration and effective data distributed to at least one of the transmission channels.
  7. 7. The method as claimed in claim 1, including an analogue overmodulation step for one of the optical signals using the transmission configuration.
  8. 8. The method as claimed in claim 1, including a reconstitution step for the digital data received by the receiver terminal configured in real time using the transmission configuration.
  9. 9. A device for transmitting digital data using a primary optical signal including a transmitter terminal and a receiver terminal; said transmitter terminal including:
    a processor including means for distributing and sending digital data over transmission channels,
    optical sources that are able to send optical signals of different wavelengths; each of the optical sources having means to modulate the optical signal of said optical source as a function of digital data sent by the processor over a transmission channel,
    a wavelength multiplexer able to generate the primary optical signal by wavelength multiplexing of optical signals sent by the optical sources;
    and further comprising:
    means for determining a magnitude characterizing optical-wave degradation between the transmitter terminal and the receiver terminal,
    a distribution module, implemented in the processor, that is able to distribute the digital data over a number of transmission channels that is less than or equal to the number of optical sources,
    a control module, implemented in the processor, that is able to determine the number of transmission channels by means of a stepwise decreasing function of the magnitude characterizing optical-wave degradation,
    activation means for a number of optical sources equal to the number of transmission channels; the primary optical signal being generated by multiplexing the optical signals sent by the optical sources thus activated; each of the optical signals being modulated by digital data.
  10. 10. The device as claimed in claim 9, in which the processor module of the transmitter terminal also includes encoding modules for digital data distributed to each of the transmission channels,
    said encoding being characterized by a variable encoding rate determined by the control module by means of a decreasing function of the magnitude characterizing optical-wave degradation,
    said encoding rate being defined as a ratio between an effective bit rate and a bit rate outputted from the encoder.
  11. 11. The device as claimed in claim 9, in which the processor module of the transmitter terminal also includes interlacing modules for digital data distributed to each of the transmission channels.
  12. 12. The device as claimed in claim 9, in which the receiver terminal includes an optical source and an optical transmission interface that are able to transmit a secondary optical signal to the transmitter terminal, and in which the means for determining the characteristic magnitude of the transmitter terminal include an optical receiver interface of the secondary optical signal that is able to receive the secondary optical signal; the magnitude characterizing optical-wave degradation between the transmitter terminal and the receiver terminal being measured by receipt of the optical signal.
  13. 13. The device as claimed in claim 9, in which the transmitter terminal includes an optical power amplifier to amplify the primary optical signal.
  14. 14. The device as claimed claim 9, in which the transmitter terminal includes a device for transmitting a tertiary signal to the receiver terminal, and in which the receiver terminal includes a device for receiving the tertiary signal; the tertiary signal carrying a transmission configuration including at least the number of transmission terminals, enabling the receiver terminal to process the effective data sent by the primary optical signal.
  15. 15. The device as claimed in claim 14, in which the tertiary signal is an optical signal with a wavelength different from the wavelengths of the optical signals carrying the effective data.
  16. 16. The device as claimed in claim 14, in which the tertiary signal is a hyperfrequency signal.
  17. 17. The device as claimed in claim 9, in which the receiver terminal includes:
    a wavelength demultiplexer that is able to generate optical signals of different wavelengths by demultiplexing the primary optical signal,
    converters that are able to convert each of the optical signals of different wavelengths into electrical signals,
    a processor, including means for recombining electrical signals to reconstitute the digital data sent by the transmitter terminal.
US14297469 2013-06-07 2014-06-05 Method and device for optical transmission at adaptive effective rates Active 2035-06-03 US9967047B2 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
FR1301304 2013-06-07
FR1301304A FR3006834B1 (en) 2013-06-07 2013-06-07 Method and optical transmission device has flow adaptive helpful

Publications (2)

Publication Number Publication Date
US20140362875A1 true true US20140362875A1 (en) 2014-12-11
US9967047B2 US9967047B2 (en) 2018-05-08

Family

ID=49322424

Family Applications (1)

Application Number Title Priority Date Filing Date
US14297469 Active 2035-06-03 US9967047B2 (en) 2013-06-07 2014-06-05 Method and device for optical transmission at adaptive effective rates

Country Status (5)

Country Link
US (1) US9967047B2 (en)
EP (1) EP2811667B1 (en)
JP (1) JP2015008459A (en)
CA (1) CA2853554A1 (en)
FR (1) FR3006834B1 (en)

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20160204866A1 (en) * 2015-01-09 2016-07-14 Don M. Boroson Ground terminal design for high rate direct to earth optical communications
US9809328B2 (en) 2014-04-22 2017-11-07 Massachusetts Institute Of Technology Attitude determination using infrared earth horizon sensors
US9813151B2 (en) 2014-08-05 2017-11-07 Massachusetts Institute Of Technology Free-space optical communication module for small satellites
US20180019807A1 (en) * 2016-07-13 2018-01-18 Space Systems/Loral, Llc Satellite System That Produces Optical Inter-Satellite Link (ISL) Beam Based On Optical Feeder Uplink Beam
US20180041275A1 (en) * 2016-08-03 2018-02-08 Space Systems/Loral, Llc Satellite system using optical gateways and onboard processing
US9923625B2 (en) 2016-07-13 2018-03-20 Space Systems/Loral, Llc Satellite system that produces optical inter-satellite link (ISL) beam based on RF feeder uplink beam
US10050699B2 (en) * 2016-07-13 2018-08-14 Space Systems/Loral, Llc Satellite system that produces optical inter-satellite link (ISL) beam based on optical ISL received from another satellite
US10075242B2 (en) 2016-06-15 2018-09-11 Space Systems/Loral, Llc High throughput satellite system with optical feeder uplink beams and RF service downlink beams
US10128949B2 (en) 2015-02-27 2018-11-13 Massachusetts Institute Of Technology Methods, systems, and apparatus for global multiple-access optical communications

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20020051284A1 (en) * 1998-02-27 2002-05-02 Kazuo Takatsu Light wavelength-multiplexing systems
US20050213966A1 (en) * 2002-04-12 2005-09-29 Martin Chown Transmission system
US20080225182A1 (en) * 2007-03-14 2008-09-18 Larry Silver Analog television demodulator with over-modulation protection
US20120282854A1 (en) * 2009-12-24 2012-11-08 Eutelsat S A Installation for emission/reception of satellite signals
US20140064304A1 (en) * 2012-08-28 2014-03-06 Optilab, Llc System and method for distributing optical signals

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2002051099A (en) * 2000-07-31 2002-02-15 Hamamatsu Photonics Kk Transmitter, receiver and transmitting/receiving system
US6731878B1 (en) * 2000-08-17 2004-05-04 At&T Corp Free space optical communication link with diversity
US20040208602A1 (en) * 2001-12-01 2004-10-21 James Plante Free space optical communications link tolerant of atmospheric interference
JP2005062510A (en) * 2003-08-13 2005-03-10 Seiko Epson Corp Toner and method for manufacturing same
US20050238357A1 (en) * 2004-04-27 2005-10-27 Farrell Thomas C Laser communication system with adaptive data rates
FR2957214B1 (en) * 2010-03-08 2012-10-26 Astrium Sas Method of optical transmission laser signals

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20020051284A1 (en) * 1998-02-27 2002-05-02 Kazuo Takatsu Light wavelength-multiplexing systems
US20050213966A1 (en) * 2002-04-12 2005-09-29 Martin Chown Transmission system
US20080225182A1 (en) * 2007-03-14 2008-09-18 Larry Silver Analog television demodulator with over-modulation protection
US20120282854A1 (en) * 2009-12-24 2012-11-08 Eutelsat S A Installation for emission/reception of satellite signals
US20140064304A1 (en) * 2012-08-28 2014-03-06 Optilab, Llc System and method for distributing optical signals

Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9809328B2 (en) 2014-04-22 2017-11-07 Massachusetts Institute Of Technology Attitude determination using infrared earth horizon sensors
US9813151B2 (en) 2014-08-05 2017-11-07 Massachusetts Institute Of Technology Free-space optical communication module for small satellites
US20160204866A1 (en) * 2015-01-09 2016-07-14 Don M. Boroson Ground terminal design for high rate direct to earth optical communications
US20160204865A1 (en) * 2015-01-09 2016-07-14 Don M. Boroson Link architecture and spacecraft terminal for high rate direct to earth optical communications
US10003402B2 (en) * 2015-01-09 2018-06-19 Massachusetts Institute Technology Ground terminal design for high rate direct to earth optical communications
US9998221B2 (en) * 2015-01-09 2018-06-12 Massachusetts Institute Of Technology Link architecture and spacecraft terminal for high rate direct to earth optical communications
US10128949B2 (en) 2015-02-27 2018-11-13 Massachusetts Institute Of Technology Methods, systems, and apparatus for global multiple-access optical communications
US10075242B2 (en) 2016-06-15 2018-09-11 Space Systems/Loral, Llc High throughput satellite system with optical feeder uplink beams and RF service downlink beams
US9923625B2 (en) 2016-07-13 2018-03-20 Space Systems/Loral, Llc Satellite system that produces optical inter-satellite link (ISL) beam based on RF feeder uplink beam
US20180019807A1 (en) * 2016-07-13 2018-01-18 Space Systems/Loral, Llc Satellite System That Produces Optical Inter-Satellite Link (ISL) Beam Based On Optical Feeder Uplink Beam
US10050699B2 (en) * 2016-07-13 2018-08-14 Space Systems/Loral, Llc Satellite system that produces optical inter-satellite link (ISL) beam based on optical ISL received from another satellite
US9979465B2 (en) * 2016-07-13 2018-05-22 Space Systems/Loral, Llc Satellite system that produces optical inter-satellite link (ISL) beam based on optical feeder uplink beam
US20180041275A1 (en) * 2016-08-03 2018-02-08 Space Systems/Loral, Llc Satellite system using optical gateways and onboard processing
US10069565B2 (en) * 2016-08-03 2018-09-04 Space Systems/Loral, Llc Satellite system using optical gateways and onboard processing

Also Published As

Publication number Publication date Type
EP2811667A1 (en) 2014-12-10 application
CA2853554A1 (en) 2014-12-07 application
EP2811667B1 (en) 2018-07-25 grant
US9967047B2 (en) 2018-05-08 grant
JP2015008459A (en) 2015-01-15 application
FR3006834A1 (en) 2014-12-12 application
FR3006834B1 (en) 2015-06-19 grant

Similar Documents

Publication Publication Date Title
Winzer et al. Spectrally efficient long-haul optical networking using 112-Gb/s polarization-multiplexed 16-QAM
US6341023B1 (en) Multiple level modulation in a wavelength-division multiplexing (WDM) systems
US6111675A (en) System and method for bi-directional transmission of telemetry service signals using a single fiber
Chagnon et al. Experimental study of 112 Gb/s short reach transmission employing PAM formats and SiP intensity modulator at 1.3 μm
US6198559B1 (en) Automatic delay compensation for generating NRZ signals from RZ signals in communications networks
US20060285607A1 (en) High availability narrowband channel for bandwidth efficient modulation applications
US6865344B1 (en) Code-switched optical networks
US6181450B1 (en) System and method for free space optical communications
US5892865A (en) Peak limiter for suppressing undesirable energy in a return path of a bidirectional cable network
US6222658B1 (en) Method and apparatus for a free space optical non-processing satellite transponder
US6185408B1 (en) Method and apparatus for mitigating the effects of a communications channel using polarized signals
EP0476569A2 (en) Mobile communication system
US6437892B1 (en) System for reducing the influence of polarization mode dispersion in high-speed fiber optic transmission channels
US7110681B1 (en) Method and apparatus for optical transmission
US20120263466A1 (en) Multidimensional hybrid modulations for ultra-high-speed optical transport
Fischer et al. Bandwidth-variable transceivers based on four-dimensional modulation formats
US6058227A (en) Method and apparatus for an opto-electronic circuit switch
Zhou et al. 400G WDM transmission on the 50 GHz grid for future optical networks
US20080002981A1 (en) Ground to space to ground trunking system
US20030072050A1 (en) Multilevel pulse position modulation for efficient fiber optic communication
US6496297B1 (en) Device and method for modulating an optical signal
US6134225A (en) Device for broadcasting digital information via satellite
US7856184B2 (en) Systems and methods for adaptive interference cancellation
US20070183791A1 (en) Multiformat transmitter
US20050135501A1 (en) Module to module signaling with jitter modulation

Legal Events

Date Code Title Description
AS Assignment

Owner name: THALES, FRANCE

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:KERNEC, ARNAUD LE;DERVIN, MATHIEU;SOTOM, MICHEL;SIGNING DATES FROM 20140711 TO 20140722;REEL/FRAME:033715/0161